Researches on an organic thin-film light emitting device in which electrons injected from a cathode and holes injected from an anode emit light when they are recombined in an organic fluorescent body held by both electrodes have been actively conducted in recent years. This light emitting device is characteristic for high luminance light emission in the form of a thin type and under a low driving voltage, and multicolor light emission due to selection of a fluorescent material, and has been paid attention.
Such researches have been studied by many research institutes since C. W. Tang et al. of Kodak Co., Ltd. showed that an organic thin-film device emits light at high luminance. A representative constitution of the organic thin-film light emitting device presented by the research group of Kodak Co., Ltd. is one such that a hole transporting diamine compound, 8-hydroxyquinoline aluminum which serves as an emissive layer, and Mg:Ag as a cathode are sequentially provided on an ITO glass substrate, and can emit green light of 1,000 cd/m2 at a driving voltage of around 10V (see Non-Patent Document 1).
Since the organic thin-film light emitting device can afford a variety of light-emitted colors by using various fluorescent materials in an emissive layer, and studies of practical realization for displays and the like have been actively conducted. Among emissive materials emitting three primary colors, a research on a green emissive material is most advanced and, currently in a red emissive material and a blue emissive material, a research has been conducted intensively aiming at improvement in properties.
It is necessary that the organic thin-film light emitting device satisfies improvement in a luminance efficiency, reduction in a driving voltage and improvement in durability. Among them, when the luminance efficiency is low, outputting of an image requiring high luminance becomes impossible, and the amount of power consumed for outputting desired luminance is increased. For example, in order to improve the luminance efficiency, a variety of emissive materials have been developed (see, e.g., Patent Documents 1 to 4). In addition, electron transporting materials having pyrene as a basic skeleton have been developed (see, e.g., Patent Documents 5 to 7). In addition, techniques of doping a material used as an electron transporting layer with an alkali metal have been developed (see, e.g., Patent Documents 8 to 12).